Explanation:
Now known to be a globular star cluster at the tender
age of 10 billion years,
M71 is
a mere 13,000 light-years
away within the narrow boundaries of the faint constellation Sagitta.
Close to the plane of the Milky Way galaxy in
planet Earth's sky, its 10,000 or so member stars are
gathered into a region about 27 light-years across near the center of
this color composite view.
In fact, the line-of-sight to M71 passes along
the galactic plane through much intervening
diffuse interstellar dust.
The dust dims starlight and scatters blue light more efficiently,
masking the brightness
of M71's stars
and shifting true star colors toward the red.
How much are the star colors shifted?
Slide your cursor over the image (or follow
this link)
to use an estimate of the dust reddening or
galactic extinction
to correct the star colors in M71.
Corrections to the brightness and colors of M71 member stars are needed
to measure the cluster's distance and age using a
Color-Magnitude diagram.